Generally, polymeric acrylic acid derivatives are formed by free-radical polymerization, using initiators which form free radicals and when two of the free radicals formed react with one another to cause chain termination, the polymerization is generally terminated. High molecular weight polymers having a very wide molecular weight distribution can be obtained by this method; however, block copolymers having a specified arrangement of the individual blocks cannot be produced in this manner.
Anionic polymerization of acrylic acid derivatives is described, for example, in U.S. Pat. No. 4,351,924 to Andrews et al, in which the polymerization is initiated by initiators which form anions, such as alkali metal-organic compounds instead of by free radicals. This type of polymerization leads to so-called "living" polymers having active terminal groups, because two ions having the same charge will not react to cause chain termination. Chain termination can be induced artificially, for example, by the addition of water or an alcohol. This process has the disadvantage that the desired narrow molecular weight distribution can be obtained only at low temperatures (down to -80.degree. C.) and with very pure starting materials.
The polymerization of acrylic acid derivatives, which is known as "quasi-ionic" polymerization is similar to anionic polymerization. In the quasi-ionic polymerization, the initial reaction is initiated by certain selected initiators together with nucleophilic or electrophilic catalysts to form "living" polymers. Selected initiators which are employed in the polymerization are silicon, tin and germanium compounds, in which the elements are linked to oxygen or carbon atoms, such as trimethylsilylketene acetals or trimethylsilyl cyanide. (See, for example, U.S. Pat. Nos. 4,414,372 to Farnham; 4,417,034 to Webster; 4,508,880 to Webster; and 4,524,196 to Farnham et al). This process can be carried out at room temperature or at higher temperatures, but it requires high purity starting materials, and in addition, forms polymers of the desired narrow molecular weight distribution only when methacrylic acid derivatives are employed.
When mercaptosilane type initiators are employed, "living" polymers of narrow molecular weight distribution are obtained under the conditions of quasi-ionic polymerization, even when acrylic acid derivatives are used as the monomers. (See, for example, U.S. Pat. No. 4,626,579 to Reetz).
Polymerization of acrylic ester monomers in the presence of a polymerization initiator comprising a tetracoordinate silicon-containing organic compound having at least one initiating site and a catalyst which is a source of fluoride, bifluoride or selected oxyanions is described in U.S. Pat. No. 4,771,117 to Citron et al. Citron discloses as initiators silanes, siloxanes and silazanes containing organic compounds having up to two silicon atoms per molecule.
According to the art, polymers having a narrow molecular weight distribution can be obtained by means of quasi-ionic polymerization of monomeric acrylic acid derivatives of any desired type using certain organosilicon compounds as initiators in conjunction with nucleophilic or electrophilic catalysts, but the average molecular weight of the polymers, are in general, relatively low.
It is, therefore, an object of the present invention to provide a process for polymerizing polar compounds which have a C.dbd.C double bond in the alpha-position to a carbonyl or nitrile group. Another object of the present invention is to provide a process for polymerizing polar compounds having a C.dbd.C double bond in the alpha-position to a carbonyl or nitrile group, in which the polymerization is initiated by organo-metallic compounds together with nucleophilic or electrophilic catalysts. Still another object of the present invention is to provide a process for polymerizing polar compounds having a C.dbd.C double bond in the alpha-position to a carbonyl or nitrile group using organo-metallic compounds and nucleophilic or electrophilic catalysts in the presence of an aprotic solvent. A further object of the present invention is to provide a process for polymerizing polar compounds having a C.dbd.C double bond in the alpha-position to a carbonyl or nitrile group at temperatures of from -100.degree. C. up to 100.degree. C. A still further object of the present invention is to provide a process for polymerizing acrylic acid derivatives to form polymers having both a high average molecular weight and a narrow molecular weight distribution.